Function stress

Write a user defined funtion that determines the principle stress for the stress components.

Here is what I did:

function [ Smax,Smin ] = princstress( Sxx,Syy,Sxy )
%This function is going to be used to calculate the principal stresses
a=(Sxx+Syy)/2;
b=sqrt(((Sxx-Syy)/2)^2+Sxy^2);
Smax=a+b
Smin=a-b
end

Does that look right?